EVS28 KINTEX, Korea, May 3-6, 2015
Rotating Transformer for a Wound Rotor Synchronous Motor
Jiyoung Lee1,2, Jongmoo Kim1, and Byoungchul Woo1 1Korea
Electrotechnology Research Institute, Changwon, Korea 2University of Science & Technology, Korea
[email protected]
Introduction
This paper presents a design of a rotary transformer to be used instead of brushes and slip-rings in 7.5kW-grade wound rotor synchronous motor for a propulsion system of electric vehicles. The basic components of the rotary transformer are pot cores and adjacent windings, which are classified into two parts- primary and secondary as the principles of general transformers. And high frequency is used to reduce the overall volume.
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Introduction There are five major design variables, which are (1) source frequency, (2) number of turns in primary winding, (3) inner diameter of winding window, (4) outer diameter of core, and (5) height of core. The design variables are optimized by Response Surface Methodology to efficiently transmit the required power. Factor experiments for the optimum design are performed by 2dimensional axi-symmetry finite element analysis (FEA). In the analysis model for the FEA, the magnetic field is connected to external circuits. The primary circuit is external power source, and the secondary circuit is linked to field winding in the wound rotor synchronous motor. The designed rotary transformer is fabricated, and the characteristic are shown by both analytically and experimentally. 3
Rotary Transformer for Exciter Rotary Transformer for Exciter in Induction machine
Cutaway of a doubly-fed induction generator with a rotary transformer [1][2]
Laboratory scheme for load tests [2]
[1] M.Ruviaro, F.Runcos, N.Sadowski, I.M.Borges, “Analysis and test results of a brushless doubly fed Induction machine with rotary transformer,” IEEE Trans. on Industrial Electronics 59(6), 2670-2677, 2012 [2] http://www.scielo.br/scielo.php?pid=S2179-10742013000200013&script=sci_arttext#f1 4
Rotary Transformer for Exciter Rotary Transformer for Exciter in Synchronous machine Synchronous Machine
Rectifier
Induction Machine
Rotor : AC field 3ph-Rotary transformer
Rotor : DC field 1~3ph-Rotary transformer
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Rotary transformer Configurations
Axial (left) and Pot core (right) rotating transformers [3][4]
[3] J.P.C.Smeets, L.Encica, E.A.Lomonova, “Comparison of winding topologies in a pot core rotating transformer,” IEEE Xplore, 2010 [4] J.Legranger, G.Friedrich, S.Vivier, J.C.Mipo, “Comparison of two optimal rotary transformer deisgns for highly constrained applications,” IEEE Xplore, 2007
Winding topologies for the pot core rotating transformer, adjacent (left) and coaxial (right) [3]
Conceptual configuration of objective model
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Design Specifications Contents
Values
Primary voltage
106.1 Vrms
Primary frequency
20~50 kHz
Secondary required voltage
66.6 Vrms
Secondary required current
3.0 Arms
Secondary power
200 W
Max rotating speed
10,000rpm
Diameter of axis
34 mm
Diameter of outmost housing
144 mm
Max axial length
78 mm
Air-gap length
1mm or less
Core material
Mn-Zn soft ferrite
Cooling
Natural cooling
Primary circuit : Phase-shift DC-DC converter
Secondary circuit : Full bridge rectifier
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Analysis Model and Design Variables Axi-symmetric model for magnetic field analysis Axis of Symmetry
Secondary coil Primary coil Secondary core Primary core Design variables (1) Cx2 (2) Cx4 (3) Ch (=Ch1=Ch2) (4) Np (No. of turns in primary) (5) Freq (Primary frequency) 8
Analysis Model and Design Variables
External circuit Independent variable 3 Independent variable 2
Objective power: 200~300W
Independent variable 1
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Response Surface Methodology
è 43 DOE samples for 5 design variables (DOE: design of experiment)
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Response Surface Methodology
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Response Surface Methodology
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Design Results [Unit: mm]
First RSM results [Variables] Freq=27.5 kHz Np = 40 turns ( Ns=26 turns) Cx1=17, Cx2=20.5, Cx4=39, Ch=6.5 (mm)
39 37 20.5 17 3.2
6.5 6.5
Axis of Symmetry
air-gap = 0.5mm (Fill factor : 60% or less)
[Characteristics] CD1(current density of primary) =3.3 A/mm2 Crms1(current of primary) =2.8A Pin(power of primary) =231.7W Pload(power of secondary) =220.9W Eff_sys(system efficiency) =95.3% Eff_mag(magnetic circuit efficiency) =98.5%
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Design Results [Unit: mm] Second RSM results
42.5 21 17 16
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Axis of Symmetry
10.5
Core outer diameter
85mm
Core inner diameter
34mm
Housing inner diameter
32mm
Primary core height
10.5mm
Secondary core height
9mm
Air-gap
0.5mm
Core thickness
4mm
No. of turn in primary
28 turn
No. of turn in secondary
18 turn
Diameter of conductor
1.4 mm
Fill factor
40%
Primary frequency
30kHz
Power of sencondary
226 W
Efficiency
95.2 %
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Magnetic Characteristics
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Fabrications (Primary & Secondary Ferrite core)
(Core + Coil)
(Core + Coil + Housing)
(Primary & Secondary coils) (Core + Coil + Housing à Epoxy molding)
(Rotary transformer + Power converter)
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Experiments
Secondary power : 300W_max
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